This invention relates to method and apparatus for making liquid silicon of high purity suitable for use in the production of vitreous silica as described in may copending application, METHOD AND APPARATUS FOR MAKING VITREOUS SILICA. Ser. No. 684,108 filed May 7, 1976, now U.S. Pat. No. 4,054,641, issued Oct. 18, 1977, and for making castings of silicon. The cast silicon may be in the form of billets for crystal pullers, in the form of tubes and boat for use in semiconductor processing equipment, in the form of infrared transmission windows, and the like.
The subject of vitreous silica is discussed extensively in the Encyclopedia of Chemical Technology, 2nd Ed. Vol. 18 by Kirk-Othmer at pages 73-105. Various types of silica glasses are discussed in the article Properties and Structure of Vitreous Silica by R. Bruckner in Journal of Non-Crystalline Solids 5(1970) 123-175. This article identifies four types of silica glasses by the manner in which they are produced and also refers to a fifth type produced in a plasma flame.
The silicon produced by the prior art processes and apparatus suffers from various disadvantages, primarily that of purity. It is an object of the present invention to provide a method and apparatus for producing liquid silicon the purity of which is limited only by that of the input materials.